The invention relates generally to marine propulsion stern drive units including an engine which is mounted on a boat hull and which supports a vertically tiltable and horizontally swingable lower unit part supporting a propeller. Such lower units are desirably trimmed relative to the boat hull and thereby to the water to obtain maximum speed and safety conditions. Such trimming effects both the relation of the boat to the water and the angle at which the propeller generates propulsive thrust. Other factors are involved in the "trim" of a boat as, for instance, passenger loading and sea conditions. Thus, one particular relationship of a propulsion unit to a boat can give good results under one set of conditions and less satisfactory results under another set of conditions. Furthermore, conditions can change when under way, as for instance, if the weather or sea condition change, or if the distribution of passenger weight changes. Accordingly, it is desirable to be able to adjust the trim under way.
It should also be noted that proper trim between a lower unit and a boat is an important safety factor when under way. In this regard, for instance, a "bow-down" condition can cause violent uncontrollable action in swells.
In addition to trim, another factor of significance with respect to vertically tiltable lower units is capability to absorb shock incident to rearward and upward swinging occurring in response to the striking of an underwater obstacle and the capacity for power tilting of the propulsion unit upwardly and downwardly relative to the trimmed running position. For example, propeller removal is facilitated by tilting the lower unit to its fully raised position and shallow water operation at reduced speeds is facilitated by tilting the lower unit to a partially raised position. Power tilting in the down or return direction to the trimmed position also affords return of the lower unit after the striking of an underwater obstacle and after power tilting upwardly to partially and fully raised positions.
Various arrangements have been provided in the past for frictionally and hydraulically absorbing shock or dissipating energy in response to the striking of an underwater obstacle. In addition, various arrangements have been employed to afford power tilting of a marine propulsion lower unit between a running position and a partially or fully raised or elevated position. In addition, various hydraulic arrangements have been provided for adjusting the trim of an outboard motor relative to a boat even when under way and to afford energy absorption in response to striking of an underwater obstacle. However, all the known prior stern drive arrangements were incapable, without trim setting by the operator, of affording propulsion unit return to the same trim position after power tilting or after tilting in response to the striking of an underwater obstacle. Attention is directed to the following U.S. patents:
Ziegler Pat. No. 3,250,240 issued May 10, 1966; PA1 Kiekhaefer Pat. No. 2,953,335 issued Sept. 20, 1960; PA1 North Pat. No. 3,295,221 issued Nov. 15, 1966; PA1 North Pat. No. 3,434,449 issued Mar. 25, 1969; PA1 Woodfill Pat. No. 3,434,448 issued Mar. 25, 1969; PA1 McCormick Pat. No. 3,434,450 issued Mar. 25, 1969.
Attention is also directed to the commonly assigned Carpenter Application Ser. No. 118,134 filed Feb. 23, 1971, and entitled "Hydraulic Power Trim and Power Tilt System for a Marine Propulsion Device".
Attention is also directed to the Shimanckas U.S. Pat. No. 3,183,880 issued May 18, 1965, and entitled "Marine Propulsion Device."